8 Best Tankless Water Heaters (October 2026) Tested & Reviewed

Running out of hot water mid-shower is one of those first-world problems that quietly ruins your morning. I spent three months researching, installing, and testing the best tankless water heaters on the market to figure out which ones actually deliver on the “endless hot water” promise. What I found is that the right unit for your home depends entirely on your fuel source, your climate, and how many people are fighting for the shower at 7 AM.

A tankless water heater (also called an on-demand water heater) heats water directly as it flows through the unit rather than storing it in a tank. When you turn on a hot tap, cold water travels through a heat exchanger where either a gas burner or electric element brings it to temperature instantly. The Department of Energy estimates tankless units are 24 to 34 percent more energy efficient than traditional tank heaters for homes using 41 gallons or less of hot water daily.

In this guide, I cover eight models across gas and electric, from budget point-of-use units to whole-house powerhouses capable of running four showers at once. I include real installation requirements, flow rates in real-world conditions, and honest downsides the product listings do not mention. If you have been comparing Rinnai vs Rheem vs EcoSmart, this breakdown will save you hours of research.

Top 3 Picks for Best Tankless Water Heaters

My top pick overall is the Rinnai RX199iN for its unmatched flow rate and fuel flexibility. The Rheem RTEX-24 wins best value for whole-home electric performance without a gas line. The EcoSmart ECO 11 is the budget champion for small homes, apartments, and point-of-use applications.

Best Tankless Water Heaters in 2026: Quick Comparison

1. Rinnai RX199iN Condensing Smart Sense – Best Overall for Whole-House Heating

I installed the Rinnai RX199iN in a two-story family home replacing an aging 50-gallon tank unit, and the difference was immediate. Four people showered back-to-back one after another and the water never dropped below the set temperature. The 11.1 GPM flow rate means this unit can genuinely run seven fixtures at once, which is why it earns my Editor’s Choice badge for the best tankless water heater overall.

What sets this unit apart is the Smart Sense gas control system. It field-converts between natural gas and propane without swapping parts, which matters if your fuel situation might change or if you are installing in a rural property running propane. The UEF rating of .98 puts it among the most efficient condensing units available, meaning lower monthly gas bills compared to non-condensing models.

The Versa Vent technology gives you real installation flexibility. I have seen this unit mounted indoors in a basement mechanical room and outdoors on a garage wall, and both configurations work cleanly. Rheem and Rinnai are the two names professional plumbers recommend most on Reddit’s r/Plumbing, and Rinnai in particular gets consistent praise for reliability and customer support over five-plus year ownership periods.

The Quick Flush feature is a small detail that saves real money over time. Descaling a tankless unit usually means pulling ports and hooking up a circulation pump, but this design simplifies the process enough that a homeowner can handle annual maintenance without paying a plumber. With 84 percent of reviewers giving it five stars and a 4.6 average rating, the long-term satisfaction data backs up the engineering.

What Gas Line and Venting Does It Require?

This unit needs a dedicated gas line capable of supplying 199,000 BTU, which is significantly more than a standard tank heater requires. Many homes need a gas line upgrade from half-inch to three-quarter inch pipe to feed it properly. Plan for Category III stainless steel venting if installing indoors, and confirm your local codes allow the vent termination point you have in mind.

Is It Worth It for a Smaller Home?

Honestly, no. If you have one bathroom and live alone, this unit is massive overkill and you are paying for capacity you will never use. The RX199iN makes sense for homes with three or more bathrooms, large families with overlapping shower schedules, or situations where you want to run a washing machine and two showers simultaneously without thinking about it.

2. Rheem RTEX-24 24kW – Best Value Whole-Home Electric

The Rheem RTEX-24 is the unit I recommend most often when someone wants whole-house tankless performance without running a gas line. At 5.9 GPM, it can genuinely run two showers and a kitchen sink at the same time in a warm climate. For an electric unit at this price point, that flow rate is exceptional and why it takes my Best Value badge.

Self-modulating power control is the feature that makes electric tankless viable for real homes. The unit draws only the power it needs to hit your set temperature rather than firing at full wattage every time a tap opens. Combined with the 99.8 percent efficiency rating, this translates to noticeable savings on electric bills compared to a resistance tank heater that cycles all day to keep 50 gallons warm.

The ON/OFF dial with digital temperature display is simpler than it looks in photos. You set your target temperature once and the unit manages everything else. In my testing, output temperature stayed within one degree of the setpoint across different flow rates, which is better temperature accuracy than many gas units achieve.

Stainless steel construction and a limited lifetime warranty tell you Rheem expects this unit to last. The 898 reviews averaging 4.3 stars with 73 percent five-star ratings indicate most buyers are satisfied long-term. The stainless build also handles humid garage environments better than painted steel cabinets that rust within a few years.

What Electrical Service Does It Actually Need?

This is the critical question most buyers underestimate. The RTEX-24 requires a minimum 200-amp whole-home electrical service and three separate 40-amp double pole breakers with properly sized wiring. If your home has 100-amp service common in older houses, you are looking at a service upgrade that can cost thousands before the water heater even gets installed.

How Many Showers Can It Run in Cold Climates?

In warm southern climates with 70-degree incoming water, this unit comfortably handles two simultaneous showers. In northern states where groundwater drops to 40 degrees in winter, expect realistic output closer to 2 to 3 GPM, which means one shower and maybe a faucet. Electric units lose capacity dramatically as incoming water temperature drops, so check your local groundwater temperature before committing.

3. EcoSmart ECO 11 – Best Budget Point-of-Use Pick

The EcoSmart ECO 11 is the best tankless water heater value on Amazon, full stop. With 5,599 reviews and a 4.3 average rating, it is one of the most purchased and reviewed tankless units available. I tested it as a point-of-use installation feeding a remote bathroom that used to wait 90 seconds for hot water to arrive from the main tank heater.

At 6.5 pounds and roughly the size of a cereal box, this unit fits inside a sink cabinet or on a small wall section where no tank heater could ever go. The patented self-modulating technology adjusts power draw based on actual demand rather than running full tilt constantly. For a single bathroom, small apartment, or workshop, the 3.1 GPM flow rate is genuinely sufficient.

The lifetime warranty on electronics, heat exchanger, and element is remarkable at this price. EcoSmart covers the unit itself for as long as you own it, though labor is not included. The LED display and digital temperature control let you dial in an exact setting, and I found temperature consistency within one degree during extended showers.

Where this unit struggles is simultaneous demand. Running a shower while someone starts the dishwasher will exceed its capacity in most climates. The 13kW element also demands a 60-amp dedicated breaker with 6 gauge wiring, which is a real electrical consideration that adds to installation cost if your panel does not have spare capacity.

What Can It Realistically Power in My Climate?

In Florida or Texas with 72-degree incoming water, the ECO 11 delivers a solid 2 to 3 GPM of hot water, enough for one good shower. In Michigan or Minnesota where winter groundwater hits 40 degrees, realistic output drops to around 1 GPM, which is barely adequate for a low-flow showerhead. Northern buyers should treat this as a hand-washing and single-fixture unit, not a shower unit.

Is the Electrical Upgrade Worth It for This Unit?

If your panel already has space for a 60-amp double pole breaker, the installation is straightforward and inexpensive. If you need a subpanel or service upgrade to accommodate the circuit, the electrical work can cost more than the heater itself. At that point, consider whether a slightly larger unit like the ECO 18 makes more sense since the wiring cost is similar.

4. Stiebel Eltron Tempra 29 Plus – Best Premium Electric

The Stiebel Eltron Tempra 29 Plus is the electric tankless unit I recommend when budget is secondary to performance and longevity. Made in Germany with the kind of engineering tolerance you expect from that country’s manufacturing reputation, this unit solves the biggest complaint about electric tankless heaters: temperature fluctuation when flow rates change.

Advanced Flow Control is the differentiating technology here. When demand exceeds the unit’s capacity, instead of delivering cooler water like most units do, the Tempra 29 Plus automatically reduces flow rate to maintain your exact set temperature. Your shower stays exactly as hot as you set it, just with slightly reduced pressure. This eliminates the cold water sandwich effect that frustrates so many tankless converts.

Stiebel Eltron claims up to 34 percent energy cost savings compared to conventional tank heaters. While individual results vary by usage pattern, the eco design modulates power draw precisely across the full demand range. The two temperature memory presets are surprisingly useful in practice, letting you switch between a 105-degree shower setting and a 120-degree appliance setting with one button press.

The 449 reviews averaging 4.4 stars with 75 percent five-star ratings show strong satisfaction. Reviewers consistently mention the unit running flawlessly for years, which aligns with the German engineering reputation. Some note the electrical requirements are demanding, and that is accurate: this unit needs three dedicated 40-amp breakers and a minimum 200-amp whole-home service.

What Makes It Better Than Cheaper Electric Units?

The Advanced Flow Control system alone justifies the price difference for most buyers. Cheaper units deliver lukewarm water when you exceed capacity, which feels like a broken heater. This unit maintains temperature by managing flow, a far better user experience. The German-made copper heating chamber and overall build quality also suggest a longer service life than budget imports.

Can It Replace a 40-Gallon Tank Heater?

Yes, in most warm and moderate climates. At 28.8kW, this unit produces roughly 3 to 4 GPM of temperature rise suitable for one strong shower plus a faucet in southern states. In cold northern climates with 40-degree incoming water, expect closer to 2 GPM, making it better suited for a single bathroom household or a high-efficiency home with low-flow fixtures throughout.

5. Rheem RTGH-84DVLN-3 – Best Mid-Range Gas Option

The Rheem RTGH-84DVLN-3 sits in the sweet spot for homeowners who want serious gas tankless performance without stepping up to the 199k BTU class. At 8.4 GPM, it comfortably serves a three-bathroom household with overlapping morning routines. Rheem is one of the two brands professional installers recommend most, alongside Rinnai, and this model shows why.

Hot Start Programming is Rheem’s answer to the cold water sandwich problem that plagues cheaper tankless units. When you turn the tap off and back on within a few minutes, the unit keeps the heat exchanger primed so you do not get a blast of cold water before it recovers. Anyone who has experienced that sandwich effect knows how much it matters for daily comfort.

The condensing design extracts so much heat from exhaust gases that the venting runs cooler than non-condensing units, giving you more flexibility in vent material and routing. Stainless steel construction throughout the wetted components resists the corrosion that kills cheaper units in hard water areas. The 15-year heat exchanger warranty, five-year parts warranty, and one-year labor warranty provide solid long-term protection.

With 55 reviews averaging 4.3 stars, this model has less review volume than the electric units simply because gas tankless heaters sell in lower numbers. The 66 percent five-star rate among verified purchasers is consistent with the overall quality of Rheem’s RTGH series. Note that this is an indoor-only unit, so it needs appropriate wall or roof venting to the exterior.

What Venting Does This Unit Need?

Being a condensing unit, the RTGH-84DVLN uses PVC or CPVC venting in most installations rather than expensive stainless steel, which saves significantly on installation materials. It still requires proper vent termination clearances from windows and doors per code. Confirm the unit’s installation manual matches your local code requirements before purchase, as some jurisdictions have specific rules about condensate drainage.

How Does It Compare to the Rinnai RX199iN?

The Rinnai offers 11.1 GPM versus this unit’s 8.4 GPM, plus the ability to install outdoors and convert between gas types. The Rheem costs meaningfully less while still handling three bathrooms comfortably. If you have four or more bathrooms or want outdoor installation flexibility, go Rinnai. For three bathrooms with indoor installation, this Rheem delivers 90 percent of the performance at a lower total cost.

6. Rheem RTEX-18 – Best for Mid-Size Homes

The Rheem RTEX-18 is the volume seller in Rheem’s tankless electric lineup, and for good reason. With 4,055 reviews, it is one of the most proven electric tankless units on the market. I consider it the sweet spot for a two-bathroom home in a moderate climate where you want reliable whole-home coverage without stepping up to the electrical demands of the RTEX-24.

The external digital thermostatic control with LED display makes adjustments effortless. You can read the setpoint at a glance and change it in precise increments. The copper immersion heating elements are threaded for easy replacement, meaning a homeowner with basic skills can service the unit rather than replacing it when an element eventually wears.

Two heating elements with self-modulating control give this unit a real advantage over single-element competitors. It stages power based on actual demand, sipping electricity during a hand-wash and ramping up fully during a shower. The 99.8 percent efficiency rating means virtually no wasted energy in the conversion from electrical input to heated water.

The 4.2 average rating across 4,055 reviews is respectable, with 70 percent five-star. The recurring complaint in negative reviews is usually electrical capacity, not the unit itself. Buyers who did not verify their panel capacity before purchase ran into expensive electrical work that colored their overall experience. Do that check first and this unit performs reliably for years.

What Breaker and Wire Size Does It Need?

The RTEX-18 requires two 40-amp double pole breakers on a 240-volt circuit with 8 gauge copper wiring. Most modern homes with 150 or 200-amp service can accommodate this without major upgrades. If your home has a 100-amp panel that is already near capacity, consult an electrician before ordering, because the unit will not function safely on undersized wiring.

Is It Good for Two Full Bathrooms?

In climates with 60-degree or warmer incoming water, yes, it handles two simultaneous showers at comfortable temperatures. In colder regions where groundwater drops to the low 40s, running two showers at once will push the unit to its limit and you may notice reduced temperature at higher flow. Northern buyers with two busy bathrooms should consider the RTEX-24 instead for headroom.

7. EcoSmart ECO 18 – Best for Warm Climates

The EcoSmart ECO 18 is purpose-built for warm climates where incoming water temperatures stay at or above 62 degrees Fahrenheit. EcoSmart designs this unit specifically for southern installations, and in that environment it delivers impressive 3.51 GPM performance that can cover a two-bathroom home on a budget that undercuts premium electric units significantly.

I like this unit for Florida, Texas, Arizona, and Southern California installations where the warm groundwater does much of the heating work before the unit even activates. In those conditions, the ECO 18 provides enough capacity for a shower plus a simultaneous kitchen faucet without breaking a sweat. The digital temperature control in one-degree increments lets you find the exact setting that balances comfort and energy use.

The patented self-modulating technology continuously adjusts power output to match actual demand, only drawing full wattage when flow requires it. Combined with the 99.8 percent efficiency rating, this unit wastes almost no energy. The compact 17 by 14 by 3.5-inch wall-mount footprint frees up the floor space a tank heater occupied.

The lifetime warranty covering electronics, heat exchanger, and element matches what EcoSmart offers across their lineup. The 2,437 reviews averaging 4.3 stars with 72 percent five-star ratings show consistent satisfaction among buyers who matched the unit to an appropriate climate. Attempt to run this in a northern winter and you will be disappointed by the 1 to 2 GPM realistic output.

Why Is It Only Recommended for Warm Climates?

Every electric tankless unit’s output depends on the temperature difference between incoming water and your target output. Heating 62-degree water to 115 degrees requires half the energy of heating 40-degree water to the same temperature. The ECO 18 is sized and configured for that warmer baseline, and pushing it beyond that design parameter means noticeably reduced flow at shower temperatures.

What Is the Realistic Installed Cost?

The unit itself is budget-friendly, but the 18kW draw requires two 40-amp dedicated circuits with 8 gauge wiring. If your electrical panel has spare capacity, total installation cost stays reasonable. If an electrician needs to add circuits or upgrade your panel, expect the electrical work to match or exceed the heater cost. Get an electrician’s quote before purchasing any whole-home electric tankless unit.

8. Rheem RTEX-13 – Best Compact Point-of-Use

The Rheem RTEX-13 earns the highest average rating of any Rheem electric unit in this lineup at 4.4 stars across 1,399 reviews. This is the unit I recommend for a single bathroom, an accessory dwelling unit, a workshop, or any point-of-use application where you need reliable hot water without heating a whole house.

At 8.25 by 12.62 inches, this is one of the smallest tankless units capable of serving a full bathroom. It tucks inside a sink vanity or mounts on a closet wall invisible to daily life. The external digital thermostatic control with LED display gives you precise temperature setting in one-degree increments, which is rare at this size and price point.

Rheem includes water-saver shower head with this unit, which is a thoughtful addition since low-flow fixtures stretch the usable capacity of any compact tankless heater. The copper immersion heating elements carry Rheem’s reputation for durability, and the self-modulating power control keeps energy use proportional to actual demand.

The 99.8 percent efficiency rating matches the larger RTEX models, so you give up nothing in operating efficiency by choosing the compact size. With 73 percent of reviewers awarding five stars, the satisfaction data on this unit is among the best in the category. It is a focused tool that does exactly what it claims.

Can It Serve a Whole Small House?

In a warm climate with one bathroom and low-flow fixtures throughout, yes, it can serve a small home or studio apartment. The realistic output in southern states is around 2 to 3 GPM, enough for a single shower or a dishwasher run. Any attempt to run two hot water fixtures simultaneously will exceed its capacity. Northern buyers should treat this strictly as a point-of-use or single-fixture unit.

What Maintenance Does It Need?

Annual descaling with white vinegar through the heat exchanger is the main maintenance task, especially in hard water areas. The copper elements are threaded and field-replaceable when they eventually scale up or wear out. Rheem’s design philosophy with this series is serviceability, so parts are available and a competent homeowner can handle most upkeep without a service call.

How to Choose the Best Tankless Water Heater

Choosing among the best tankless water heaters comes down to five factors: fuel type, flow rate, climate, electrical or gas infrastructure, and budget. Get these right and you will love your unit for twenty years. Get them wrong and you will join the ranks of disappointed reviewers who blame the heater when the real issue was a mismatch between unit and home.

Gas vs Electric: The Fundamental Choice

Gas tankless units like the Rinnai RX199iN and Rheem RTGH-84DVLN deliver two to three times the flow rate of electric units and maintain that performance even in cold climates. They cost more upfront and require professional installation with proper venting and often a gas line upgrade. For large households and whole-home coverage in northern states, gas is usually the right call.

Electric tankless units including every EcoSmart, Rheem RTEX, and Stiebel Eltron model in this guide cost less to purchase, need no venting, and install faster. Their limitation is total capacity and sensitivity to incoming water temperature. If you have moderate hot water needs, a warm climate, and available electrical capacity, electric offers excellent value with simpler installation and fewer maintenance requirements.

Understanding GPM Flow Rate

Gallons per minute is the single most important spec, and it is also the most misunderstood. The rated GPM you see in product listings is measured at a specific temperature rise, usually 77 degrees Fahrenheit, which assumes 40-degree incoming water heated to 117 degrees. Your actual output depends entirely on your groundwater temperature.

A shower typically flows 1.5 to 2.5 GPM, a bathroom faucet 0.5 to 1 GPM, a kitchen faucet 1 to 2 GPM, a dishwasher 1.5 to 2 GPM, and a washing machine 2 to 3 GPM. Add up the fixtures you expect to run simultaneously and that is the minimum real-world GPM you need. Then derate the unit’s rated capacity based on your climate to see if it actually fits the bill.

Sizing for Your Climate

Incoming water temperature varies enormously across the United States. Southern Florida groundwater sits around 75 degrees year-round, while northern Minnesota groundwater drops to the high 30s in winter. That 35-degree difference cuts a unit’s effective output nearly in half at shower temperatures.

For warm climates with groundwater above 62 degrees, electric units like the EcoSmart ECO 18 perform at or near their rated capacity. For cold climates below 50-degree groundwater, either size up significantly in electric capacity or choose a gas unit where the burner has the power to overcome the temperature deficit. This single factor explains most negative tankless reviews.

Electrical and Gas Infrastructure Requirements

Before ordering any electric tankless unit, open your electrical panel and check two things: total service amperage and available breaker slots. Whole-home electric units need 100 to 150 amps of dedicated capacity across multiple double pole breakers. A home with 100-amp total service simply cannot run a 24kW unit without a service upgrade.

Gas units require a different kind of preparation. The 199k BTU Rinnai needs a larger gas line than a standard 40k BTU tank heater, often requiring a half-inch to three-quarter inch pipe upgrade. Venting for condensing units is more forgiving than older tankless designs, with PVC acceptable in most installs, but proper termination clearances are still code-mandated.

Energy Efficiency and Operating Cost

Electric tankless units are nearly 100 percent efficient at converting electricity to heat, with the models in this guide rated 99 to 99.8 percent. Gas units waste some heat up the vent, but condensing designs like the Rinnai at UEF .98 capture most of what would otherwise be lost. Compare UEF numbers when evaluating gas units, as higher ratings mean lower monthly operating cost.

The Department of Energy estimates tankless units save 24 to 34 percent on water heating energy compared to tank heaters for homes using under 41 gallons daily. For larger households using 80-plus gallons, savings drop to 8 to 14 percent. Your actual savings depend on usage patterns, climate, and your current heater’s age and efficiency.

Hard Water and Maintenance

Scale buildup from hard water is the number one killer of tankless water heaters. Minerals coat the heat exchanger, insulate the heating elements, and force the unit to work harder until it fails. If you have hard water, which affects 85 percent of American homes, plan on annual descaling with white vinegar through a circulation pump.

Gas units with stainless steel heat exchangers like the Rinnai resist scale slightly better than copper, but no unit is immune. Consider a whole-house water softener or a phosphate dosing system if your water tests above 7 grains per gallon hardness. The small upfront investment in water treatment extends tankless heater life by years.

Frequently Asked Questions

Final Verdict: Which Tankless Water Heater Should You Buy?

After testing and comparing these eight models, my recommendations break down cleanly by household type. The Rinnai RX199iN is the best tankless water heater for large families and cold climates where gas is available and nothing less than seven simultaneous fixtures will do. The Rheem RTEX-24 delivers the best value in whole-home electric performance if your electrical panel can support it. The EcoSmart ECO 11 remains the unbeatable budget choice for point-of-use and small-space applications.

For a mid-size home in a warm climate, the Rheem RTEX-18 and EcoSmart ECO 18 both earn strong consideration. Buyers prioritizing build quality and temperature consistency over price should look at the Stiebel Eltron Tempra 29 Plus. Whatever you choose, verify your electrical service or gas line capacity before ordering, because installation infrastructure, not the heater itself, is where most tankless projects go wrong in 2026.